Field of the Invention
The present invention relates to an exposure control apparatus that performs photometry using a charge-accumulation type image sensor.
Description of the Related Art
A photometry range required of an image capturing apparatus such as a digital camera or digital video camera is generically about −5 to +15 in a BV value of the APEX unit. That is, the dynamic range of the photometry range is about 20 steps. On the other hand, a dynamic range that can be expressed by one accumulation of a charge-accumulation type image sensor is about 10 steps.
There is known a technique of combining image signals obtained by capturing the same scene a plurality of times under different exposure values using a charge-accumulation type image sensor, thereby generating an image having a dynamic range wider than that implemented by one accumulation (image capturing). In general, this technique is called HDR (High Dynamic Range) combination.
For example, in Japanese Patent Laid-Open No. 6-130462, a photometric apparatus using a charge-accumulation type light-receiving element alternately performs photometry with a long charge accumulation time and photometry with a short charge accumulation time, thereby obtaining photometric values from a low brightness portion to a high brightness portion even if the brightness difference in the field is very large.
In Japanese Patent Laid-Open No. 2008-113029, two photoelectric conversion elements of different saturated exposure amounts are used, thereby expanding the dynamic range.
However, when photometric calculation is performed for an image with an expanded dynamic range as described in Japanese Patent Laid-Open Nos. 6-130462 and 2008-113029, the data amount of each pixel output becomes large. When performing integration processing and multiplication processing using the pixel outputs, the circuit scale becomes large, and the processing time is prolonged.